I was planning to buy a Refurbished 2012 Mac Pro 3.2GHz Quad-Core and upgrade the HD to SSD plus 16BG RAM. This will cost me about 3k. For the same amount of money I can get Refurbished 15in 2.7GHz cMBP 2012 and upgrade it to 512Gb SSD and 16GB RAM.

I have two great external monitors (EIZO & NEC) which I can connect to laptop. That is the reason I do not consider iMac.

Which would be more reasonable option? What are your thought? Thank you!

For most design work a Macbook pro i7 is perfect as long as you don't need more than 16GB RAM for your work. Design requires lots of short cpu bursts and an SSD is also very helpful thanks to Adobe's crap optimization-ing. The MBP and current i7 3.4GHz iMac are faster than the Mac Pro if you can work within their inherent confines. A video editor would be better served by the Mac Pro regardless of the slight speed advantage the new chips have.

CPU performance would be better. I have an i7-950 (first generation i7, like Mac Pro. The Mac Pro just has a Xeon stamp on the CPU, performance is the same as regular i7) overclocked to 3.8ghz and it benches just a hair higher than my 2.3ghz Ivy Bridge in CPU performance. The MacBook Pro also has SATA 3 so you'll be able to max out the performance of your SSD, unlike the Mac Pro's SATA 2 which maxes around 275MB/s.

Memory performance is higher on the Ivy Bridge chip with both running 1600mhz memory.

The benefit of the Mac Pro is it's upgradability, but that's about it. Unless you need four hard drives, which you could do with a Mac Pro with Thunderbolt, or PCI-e slots or more than four physical cores, buying a Mac Pro today is a waste.

Depending on the resolution of your display, you may need a minidisplay port to dual link DVI adapter, keep that in mind.

Yes.
32-bit Geekbench. 64-bit has higher score for each but same disparity. A 2.7 i7 is really a 3.5GHz Quad core when all turbo is firing. 3.7GHz when single threaded tasks are all that is needed. Otherwise it idles in a much lower clock state.
MBP 2.7GHz: 12300
Mac Pro 3.2GHz: 9840